Apparatus for quantitative determination of total base or acid number of oil

- Dexsil Corporation

The total base number of an oil sample of measured volume is determined by solvating the oil sample, adding a predetermined amount of acidic species to the solvated sample to react the acidic species with any basic species contained in the oil sample, extracting the remaining acidic species into an extractant phase, separating the extractant phase from the oil sample, and measuring the acidic species content of the extractant phase to determine the quantity of basic species in the oil sample. The same technique may be used to determine the total acid number of an oil sample by adding a predetermined amount of basic species to the sample and measuring the basic species content of the extractant phase. Apparatus comprising a test kit for carrying out the method comprises a sampling syringe (10) for drawing a fixed volume of sample oil, a reaction container (22) containing premeasured quantities of acidic species and solvent in first and second frangible ampules (28, 30) and a titration container (32) containing a pH indicator in a third frangible ampule (38). A titration syringe (50) contains a basic solution for titrating the extractant and bears graduations (55) which are scaled and numbered to indicate the total base number of the sample, and a cap (56) for securing the titration syringe (50) to titration container (32).

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Description
BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the testing for basic species present in oil, and more specifically to an apparatus for determining the total base number of a sample of oil.

Generally, additives such as anti-oxidants are often incorporated by the manufacturer into lubricating oils to extend the useful life of the oils. These additives are commonly alkaline, i.e., basic, chemical species (sometimes herein referred to as "basic species") which serve to alleviate the undesired effects of acidic species which may form under the operating conditions of the engine or other device lubricated by the oil. Over the course of extended use, the basic additives can be consumed or degraded, resulting in the build-up of acidic contaminants. Of course, lubricating oils which contain no or very little akaline additives are also subject to the build-up of acidic contaminants therein. The continued use of lubricating oil containing significant concentrations of such acidic contaminants can cause corrosive damage to the engine or other mechanism it is intended to lubricate. Accordingly, it is often desired to examine the condition of lubricating oil periodically to determine whether the oil is spent and needs replacement.

Gasoline, diesel oil and other liquid hydrocarbon fuels contain varying levels of sulfur or sulfur compounds, from negligible quantities to 5 percent by weight or higher. Accordingly, one of the products of combustion in the normal operation of, e.g., internal combustion engines powered by combusting such fuels, is sulfur dioxide which is usually exhausted from the cylinders in a gaseous state. However, when sulfur dioxide reacts with water vapor present in the combustion gases, it will form sulfurous acid which readily becomes oxidized to sulfuric acid, a corrosive by-product. Therefore, basic species additives such as calcium salicylate are often added to engine lubricating oils to combat the corrosive characteristics of sulfuric acid. The sulfur level in the fuel will usually determine the usable lifetime of the lubricating oil. That is, a high sulfur content of the fuel can destroy almost all of the base additives in relatively few hours of use. Consequently, tests for the total base number ("TBN") value of lubricating oils have been devised in order to assess the corrosiveness of the oil. Thus, in the case of oils which contain basic species additives, it is desired to measure the reserve alkalinity, i.e., to measure the quantity of the basic species additives in, or remaining in, the oil. For oils which are not formulated with or no longer contain basic species additives, it is desired to measure the quantity of corrosive acidic species contained in the oil to assess the amount of corrosives build-up. Consequently, tests for the total acid number ("TAN") value of lubricating oils have been devised in order to assess the corrosiveness of such oils. Usually, the TAN is of concern with respect to oils which are employed as lubricants in devices other than internal combustion engines. Accordingly, it is sound practice to periodically check the TBN of lubricating oils used in equipment, especially engines, such as the internal combustion engines of construction equipment, trucks, ships, etc., and to check the TAN of lubricating oils used in equipment other than internal combustion engines, such as compressors and gear boxes, to determine when the oil needs to be changed. The need for an oil change is indicated by a low TBN or a high TAN. The TBN is a number scale giving the quantity of acid, expressed in terms of mg of KOH equivalents per gram of oil sample; the TAN is a number scale giving the quantity of base, also expressed in terms of mg of KOH equivalents per gram of oil sample. In order to avoid damage to engines or other lubricated devices due to deterioration of the lubricating oil, it is highly preferable to be able to chemically determine the condition of the lubricating oil before degradation of the oil is visually evident. The alternative is the wasteful, and expensive, procedure of replacing lubricating oils at short intervals based on worst-case operation scenarios or placing the equipment at risk due to corrosion. The above discussion applies as well to oils used for purposes other than lubrication, as long as the corrosiveness of the oil is of concern.

2. Related Art

European Patent Publication 170,466, published Feb. 5, 1986, discloses a method and test kit for determining the alkalinity of oil. The method is colorimetric and is practiced by placing a fixed volume of an indicator solution comprising halogenated hydrocarbons in a titration container with a known amount of sample oil. The two are mixed together by shaking, and aqueous acid is added in fixed aliquots until a specific color change is brought about in the aqueous phase. The halogenated hydrocarbons in the indicator solutions make the density of the oil phase greater than that of water, so that the aqueous phase separates as the top layer.

U.S. Pat. No. 4,203,725 to Snowden, Jr. et al, dated May 20, 1980, discloses a method and test kit for detecting the presence of contaminants in oil. This is accomplished by taking a sample of oil and adding a solvent-reagent solution. In the case of determining acidic or basic contaminants, the solvent is water (see column 8, lines 44-45) and the reagent is a pH indicator (see column 2, lines 48-56). The solvent-reagent solution is added to and mixed with the oil sample, and the mixture is allowed to separate. The color of the indicator in the lower, aqueous layer is observed and may be compared to a color scale to determine the contaminant content of the sample.

Several current Test Methods of the American Society for Testing and Materials ("ASTM"), Test Methods D 2896-88, D 974-87, D 4739-87 and D 664-89, disclose methods for the determination of TBN and TAN in petroleum products by forward and backward titrations with various acids. The D 2896-88 procedure involves the use of a potentiometric titration system, the use of powerful and dangerous reagents including perchloric acid, glacial acetic acid, sodium perchlorate and chlorobenzene, and is designed to be carried out in a laboratory environment. The D 664-89 procedure is a method for determining total acid number ("TAN") and the D 4739-87 procedure is a TBN technique utilizing an electrode based titration. The D 974-87 method uses less hazardous chemicals, but is a colorimetric test that cannot be used on dark colored oils which constitute the majority of used lubricating oils. More specifically, ASTM D 974-87 discloses a titration method for determining the TBN or TAN of a sample of oil. Part 11 of this procedure, relating to a determination of strong acid number, teaches the taking of a fixed volume of sample, adding water, mixing the water with the oil sample, removing the water, adding an indicator (methyl orange) and titrating the water with a basic solution to determine the acid number. This test is limited to use with petroleum products which are soluble or nearly soluble in mixtures of toluene and isopropyl alcohol and is not suitable for measuring the basic constituents of many basic additive-type lubricating oils (see section 1.1, and note 2). This reference also teaches the determination of acid and base numbers by titrating a single phase comprising the sample and a "titration solvent" comprising toluene, isopropyl alcohol and about 5% water. See sections 9, 7.7, and 10.

U.S. Pat. No. 3,510,260 to Krawetz et al, dated May 5, 1970, discloses a method for determining acid content of an oil sample comprising taking a sample of the oil and adding a predetermined amount of base dissolved in an immiscible solvent (see column 2, lines 25-31). An oil diluent is also added, and the three components are mixed and allowed to separate. An indicator solution is added, and the color of the separated, immiscible layer is observed. This Patent teaches that the process may be reversed to test for basic species (see column 2, lines 44-52) and that by providing an immiscible layer in which to observe the color of the indicator, the difficulty of observing the color of darkened oil is avoided (see column 2, lines 53 through column 3, line 5 and column 3, lines 29-39).

A portable TBN test offered by Mobil Corporation is presently commercially available and involves the use of glacial acetic acid and petroleum distillates. It is designed to cover a limited TBN range and requires a predetermined estimate of the expected TBN value of the oil in order for the colorimetric end point to work effectively. Determination of the end point is difficult when dirty or contaminated oils are used and the instructional procedures recommend that a flashlight be used to determine the colorimetric end point. It is not designed to be operated or handled by relatively untrained persons. For obvious reasons of time and economy, it is desirable to be able to have relatively untrained persons field test the TBN of any lubricating oil at its point of use.

SUMMARY OF THE INVENTION

The present invention provides an apparatus for determining the quantity of acidic or basic resident species present in an oil sample. The apparatus comprises a sampling means, a container system and a pH measuring means. The sampling means is for drawing a predetermined quantity of oil as a sample and introducing the sample into a reaction container. The container system comprises (i) a reactant container comprising a predetermined quantity of a reactant species comprising one of an acidic species and a basic species, for reacting with a basic or acidic resident species in the sample, if any; (ii) an extractant container containing a predetermined quantity of an extractant in which the reactant species is soluble but which is immiscible with the sample, for extracting unreacted reactant species from the sample; and (iii) a reaction container dimensioned for receiving the sample from the sampling means and for receiving the predetermined quantity of the reactant species, to allow the reactant species to be mixed with the sample, and for receiving the extractant to allow the extractant to be mixed with, and to separate from, the sample to extract the unreacted reactant species from the sample. The pH measuring means is for determining the pH of the extractant.

According to one aspect of the present invention, the pH measuring means may comprise a titration syringe containing a titrant for the reactant species, for titrating a predetermined quantity of the extractant having unreacted reactant species therein, and an indicator container containing a titration end point indicator for indicating the end point of the titration of the extractant with the titrant. The at least one reaction container may be dimensioned for further receiving the titrant and the end point indicator.

Optionally, the titration syringe may bear graduations that indicate one of the total base number and total acid number of the sample at the end point of the titration of reactant species in such predetermined quantity of extractant after reaction of said predetermined quantity of the reactant species with a sample drawn with the sampling means and extraction of remaining reactant therefrom by the extractant.

According to another aspect of the invention, at least one of the reactant container and the extractant container may comprise a frangible ampule.

According to another aspect of the invention, the apparatus may further comprise a solvent container containing a premeasured quantity of a solvent for mixing with the sample to produce a solvent phase to which the reactant species is added.

Still another aspect of the invention provides that the apparatus may comprise a second reaction container for receiving and holding the extractant, the titrant and the titration end point indicator separate from the sample during the titration.

As used herein and in the claims, "basic species" and "acidic species" have the following meanings. The term "basic species" is used to broadly mean not only strong bases but to include other compounds or substances which are suitable for use as additives in lubricating and other oils and capable of reacting with or otherwise neutralizing the corrosive effect of acids and acidic species which accumulate in or otherwise are contained within such lubricating and other oils. The term "acidic species" is used to broadly mean not only strong acids but to include other compounds or substances which exhibit corrosive properties in lubricating or other oils and which are neutralizable by basic species so as to eliminate or ameliorate their corrosive properties.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-5A collectively show the components of one embodiment of a test kit according to the present invention, each component being shown in an elevation view save for FIG. 4, wherein:

FIG. 1 shows a sampling syringe;

FIG. 2 shows, in partial cross section, a flexible reaction container containing two frangible ampules containing, respectively, a solvent and an alcoholic acid, and having a sealable spout;

FIG. 3 shows a flexible titration container having a fixed volume indicator and containing two frangible ampules containing, respectively, an extractant and a pH indicator;

FIG. 4 is a perspective view of a filtering funnel;

FIG. 5 shows, in partial cross section, a titration syringe (including the plunger of FIG. 5A assembled thereto) dimensioned and configured to be secured to the titration container of FIG. 3; and

FIG. 5A shows a plunger for use as part of the titration syringe of FIG. 5 and, in partial cross section, an exploded view of the plunger head shown in FIG. 5 and forming part of the titration syringe of FIG. 5.

DETAILED DESCRIPTION OF THE INVENTION AND SPECIFIC EMBODIMENTS THEREOF

The present invention provides an apparatus for evaluating the total base number ("TBN") or the total acid number ("TAN") of a sample of oil, such as a used lubricating oil. Generally, the apparatus and method of use of the present invention are substantially identical with respect both to testing for TBN and TAN except that, naturally, different reactants, titration liquids, etc., are employed. For economy of expression, the bulk of the following discussion will be related to those embodiments of the invention which pertain to the determination of TBN, although it will be appreciated that the same principles apply to the apparatus as used for the determination of TAN.

The apparatus of the present invention includes a sampling means for taking an oil sample of known volume. The apparatus includes several containers, some of which hold reagents used in the method aspect of the invention. Other containers are used for receiving and holding the oil sample and test reagents during the test, as described more fully below.

The oil to be tested may be taken in any convenient manner, for example, by drawing some oil from an engine crankcase into a suitable container such as a cup or can, and then using a sampling means, such as the sampling syringe illustrated in FIG. 1, to draw a measured sample of the oil. Many lubricating oils contain corrosion inhibitors and oxidation inhibitors which will react with a strong acid, especially a Bronsted-Lowry acid such as hydrochloric acid, and thus constitute resident "basic species" as that term is used herein and in the claims. Typical corrosion inhibitors are zinc and other dithiophosphates, metal sulfonates, overbased metal sulfonates, metal phenate sulfides, overbased metal phenate sulfides, acid phosphate esters, etc. Oxidation inhibitors include zinc dithiophosphates, metal dithiocarbamates, hindered phenols, phenol sulfides, metal phenol sulfides, metal salicylates, aromatic amines, dilauryl selenide, etc.

The measured sample of oil is deposited in a reaction container where it is contacted with a predetermined amount of a reactant species which is generally a suitable acid, sometimes here and in the claims referred to as an "acidic species". The apparatus includes a reactant container such as a vial, a frangible ampule or the like, that holds a predetermined quantity of the reactant species that is deposited into the mixing container for this purpose. The acidic species reagent may be an alcoholic acid solution, that is, a strong acid such as hydrochloric acid in an alcohol vehicle such as an isopropyl alcohol vehicle. If a resident "basic species" such as the alkaline additives added by oil manufacturers to lubricating oils is present in the oil, it reacts with and consumes some or all of the acidic reactant species added to the sample.

Preferably, the oil sample is first mixed with a solvent in which the oil sample and the resident basic species, if any, contained therein are soluble, to provide a solvent phase in which the oil and basic species are dissolved, and to which the predetermined amount of acidic reactant species is added. The solvent may be, e.g., isoctane, and the solvent phase provides a reaction medium which enhances the reaction of the basic species components of the oil sample with the acidic reactant species added in the test and facilitates clean extraction of acidic reactant species from the solvated, reacted oil sample. The use of a solvated oil sample also facilitates subsequent phase separation of the oil residue and an extractant, e.g., an aqueous extractant, as discussed below. The term "sample phase" as used herein refers to either a solvent phase comprising oil dissolved in a solvent or the oil sample without a solvent, as appropriate.

The acidic reactant species which remains after the addition of the reactant species to the sample phase is then extracted into a liquid extractant in which the reactant species is soluble but which is immiscible with the sample phase, i.e., is immiscible with the oil or, when a solvent is used to provide a solvent phase, is immiscible with the resulting solvent phase. For this purpose, the apparatus includes an extractant container, i.e., vial, ampule, etc., that contains a predetermined quantity of a suitable extractant which is poured into the reaction container. Preferably, the extractant is an aqueous extractant which can be mixed with the sample phase and which thereafter separates from the sample phase to form a distinct layer of an extractant aqueous phase. A clean phase separation of the solvated hydrocarbon residue and the aqueous phase having the resultant acid dissolved therein enables a more complete recovery of the resultant acid and the concomitantly greater accuracy in determining the total base number of the sample phase. However, a suitable non-aqueous extractant may be used, provided that the acidic reactant species is soluble in the extractant, and that the extractant is immiscible with the sample phase.

The quantity of acidic species which survives the reaction with the basic species and therefore is available for extraction into the extractant phase will be determined by the quantity of basic species in the oil sample tested. Therefore, the acid level of the extractant phase is indicative of the quantity of basic species remaining in the oil sample. For this purpose, the apparatus includes a pH measuring means. The pH measuring means may comprise a pH meter or any other suitable instrument may be used to determine the acid content of the extractant phase. A pH meter is perhaps more appropriate for use in a laboratory environment whereas a liquid titration provides a technique which is better suited for use in a field test kit, as titration and the color-change end point is simpler for untrained personnel to use. Accordingly, in a preferred embodiment of the present invention, the pH measuring means of the apparatus comprises a titration syringe that contains a suitable titration liquid and an indicator container containing a pH titration end point indicator. Preferably, after a fixed quantity of the extractant is thoroughly mixed with the sample phase, a specific, measured quantity of the extractant is drawn into a separate, second reaction container, and the pH indicator is added to the premeasured quantity of extractant in the second reaction container. The acid content of the extractant is then determined by using the titration syringe which contains a basic titration liquid and which may have conventional volumetric graduations marked thereon. In the case of determining the basic species content of an oil sample, the titration liquid may be an aqueous solution of a strong base, e.g., sodium hydroxide or potassium hydroxide. At the end point of the titration, the pH of the extractant will be known, and from this the total base number of the sample can be determined by calculations familiar to those of ordinary skill in the art. By allowing the user to observe the pH indicator and titration end point in an extractant which is separated from the sample phase, observation of the pH indicator is facilitated because the sample phase, which is usually quite dark and opaque in the case of a used lubricating oil or the like, would obscure the color and color change of the pH indicator if the extractant were to be titrated while in contact with the sample phase. In a preferred embodiment of the invention, however, the graduations on the syringe are scaled and labeled so that the total base number of the sample can be read directly off the syringe at the titration end point. This requires that the graduations on the syringe indicate known volumes of titration liquid and that the calculations mentioned above be performed taking at least some of the indicated volumes as end points so that at least some of the graduations can be labeled with the TBN they indicate if they correspond to the end point of the titration. Alternatively, standard volume graduations may be used and a suitable conversion chart may be provided which relates the volume of titration liquid expelled to the total base number or, in the case of an apparatus designed to determine the acidic species content of an oil sample, to the total acid number.

The titration syringe may incorporate a cap member dimensioned and configured to serve as a closure for the container in which the titration is performed. When the cap member of the titration syringe is in place as a closure on the titration container, the spout of the syringe is disposed within the interior of the container so that the contents of the syringe may then be added to the extractant phase to perform the titration. The cap member of the titration syringe and the titration container are so dimensioned and configured that the cap member closes and seals the titration container, positions the spout for introduction of titration liquid into the titration container, and seals the titration container so that nothing (except titration liquid) can enter and nothing can be spilled therefrom. This permits shaking of the titration container while injecting titration liquid therein in order to enhance the accuracy of the titration step.

The present invention provides an apparatus in which at least some of the reagents necessary to carry out this process are conveniently premeasured and stored in containers, e.g., vials, ampules or the like, so that the user may release the reagents and carry out the titration without jeopardizing the accuracy of the test due to pillage, measuring errors and the like. Use of a titration syringe bearing graduations which are scaled and numbered to directly indicate the total base number of the sample at the end point of the titration obviates the need for the user to perform any computations to interpret the results of the test. The apparatus is therefore readily usable by persons unskilled in laboratory analysis techniques and may be used in the field by untrained persons by simply following relatively simple (as compared to laboratory analyses) instructions.

In a specific embodiment, a test kit according to the present invention includes a sampling syringe 10 (FIG. 1) having a cylinder portion 12, a spout portion 14 and a plunger 16. Plunger 16 and cylinder portion 12 are dimensioned and configured so that a sample drawn by the full travel of plunger 16 within cylinder portion 12 provides a precisely measured sample of known volume, e.g., 0.37 ml. Once the sampling syringe 10 is filled with an oil sample, suction sufficient to hold the oil sample in place within the syringe is maintained simply by leaving the plunger undisturbed in place. The kit further includes a resilient reaction container 22 (FIG. 2) of generally test tube-shape into which the oil sample taken is deposited. Reaction container 22 contains the solvent (e.g., 1.0 ml of isooctane) in a first frangible ampule 28 and a predetermined amount of an alcoholic acid (e.g., 1.0 ml of 0.114N HCl in isopropyl alcohol) in a second frangible ampule 30. The hydrochloric acid content of second ampule 30 provides an acidic species to react with basic species provided by the usual alkaline additives in, or remaining in, the oil sample, if any. Both ampules 28 and 30 in reaction container 22 are supported by ampule holder 26 comprising a stiff but flexible split tube within which ampules 28 and 30, which are of a diameter somewhat greater than the inside diameter of the split tube, are retained by the gripping pressure of the split tube. Ampule holder 26 is supported by a leg portion (unnumbered) thereof which is seated at the bottom end of reaction container 22. Reaction container 22 is sufficiently resilient so that the user may crush frangible ampules 28 and 30 to release the contents thereof by squeezing the outside of reaction container 22. Reaction container 22 is made of any suitable resilient material which is sufficiently transparent to permit visual observation of the contents of reaction container 22, to observe mixing and separation of the reactants, etc., as described below. Screw threads 22b are formed adjacent to and extending from the mouth 22a of reaction container 22 so as to enable container 22 to threadably receive a screw-on cap 24. Cap 24, which serves to close container 22, is removable and replaceable on container 22 and is fitted with a valve spout 24a having a spout conduit 24b extending therethrough, and has a cap conduit 24c formed therein. Valve spout 24a is pivotably mounted within cap 24 so that it is pivotable, as indicated by the unnumbered arrow in FIG. 2, between a closed position shown in solid line rendition in FIG. 2 and an open position shown in phantom outline in FIG. 2. In the closed position illustrated in FIG. 2, spout conduit 24b is out of alignment with cap conduit 24c and seated against an interior wall (not numbered) of cap 24 whereby spout conduit 24b is sealed against flow therethrough. In the closed position illustrated, valve spout 24a is flush with the flat top 24d of cap 24. In the open position shown in phantom outline in FIG. 2, valve spout 24a is disposed at right angles to top 24d of cap 24 and spout conduit 24b is in alignment with cap conduit 24c which extends through hemispherical base portion 25 of cap 24 to allow fluid flow from the interior of container 22 through cap 24.

In use, a measured sample of the oil to be tested is taken, for example by drawing a quantity of oil from an engine crankcase and thoroughly mixing the sample. Sampling syringe 10 is then inserted into the thoroughly mixed oil sample and plunger 16 thereof is drawn fully back to fill sampling syringe 10, taking care that no air bubbles are formed within the syringe. Alternatively, the oil sample quantity may be taken by weighing the oil sample. However, a volumetric sampling technique is simpler to carry out, especially in a field test kit designed for use by relatively untrained persons. If there are air bubbles, the sample is expelled and a fresh sample taken to completely fill the syringe so that a measured quantity of oil sample is obtained. The exterior of the syringe tip inserted into the oil is then wiped clean to remove therefrom excess oil which might otherwise get into container 22 and thereby increase the size of the sample introduced into container 22 beyond the premeasured quantity contained within the cylinder portion 12 of syringe 10. The user removes cap 24 from reaction container 22 and deposits the sample oil from sampling syringe 10 into reaction container 22 by positioning spout 14 of syringe 10 in the mouth 22a of reaction container 22 and depressing plunger 16 to expel the entire measured oil sample from syringe 10 into the reaction container 22. The user then discards syringe 10 and replaces cap 24 with valve spout 24a in the closed position.

While it is possible to add the acidic species reagent directly to the sample oil, it is preferable to first solvate the sample oil by adding a solvent in which the oil sample and the basic species contained therein are soluble. The solvent dissolves the oil sample to produce a solvent phase having a lower viscosity than the oil. The lower viscosity of a sample phase comprising solvated oil, together with the use of an acidic species of enhanced miscibility (relative to an aqueous acidic species) with the solvent phase, e.g., HCl in isopropyl alcohol, facilitates completion of the reaction between any basic species in, or remaining in, the sample phase and the added acidic species reagent.

To add the solvent to the measured oil sample, the user squeezes container 22 to crush first frangible ampule 28, thus releasing the premeasured quantity of isooctane solvent into container 22. The sample oil and solvent are mixed together by shaking the container. The user then squeezes container 22 to crush second frangible ampule 30, thus releasing the premeasured quantity of alcoholic acid (HCl in isopropyl alcohol) and again shakes the container 22 to thoroughly mix the contents. Some or all of the acidic species, i.e., the HCl, reacts with and is mutually consumed by the basic species, if any, present in the oil. By providing the acidic species in an alcohol vehicle, the miscibility of the acid with the sample phase is enhanced as compared to an aqueous acid solution. The enhanced miscibility of the acidic species facilitates the degree of completion of the reaction between the basic species, if any, contained in or remaining in the oil sample to be tested, and the acidic species introduced in the test. Generally, alcohols having carbon chains of at least three carbon atoms, i.e., C.sub.3 or higher alcohols, are preferred because of their greater miscibility with oil than that of C.sub.1 or C.sub.2 alcohols.

As to the choice of acid to be used as the acidic species to react with the basic species present in the oil, the strength of the acid, i.e., its ability to react with and neutralize basic species contained in the oil, will of course affect the TBN determined by the test. Those skilled in the art will appreciate that this factor, the strength of the acid utilized, must be taken into account in assessing the meaning of the TBN number obtained. Conventionally, a strong acid such as hydrochloric acid or perchloric acid is utilized in the test to provide generally accepted TBN values for lubricating oils. However, other acids may be used, including sulfuric acid or nitric acid.

The kit further contains a resilient, second reaction container or "titration container" 32 (FIG. 3) which includes a measured quantity of liquid extractant 42 in which the acidic species is soluble but which is immiscible with the sample phase, whether the oil sample is solvated or not. The amount of extractant provided is greater than that required to carry out the titration portion of the test, for reasons described below. Titration container 32 holds a pH indicator in an indicator container shown as a third frangible ampule 38, which is supported by an ampule holder 36 similar to ampule holder 26 in reaction container 22. The indicator, which may comprise 200 microliters of conventional methyl red solution, is released into the extractant phase by crushing third ampule 38 by squeezing resilient titration container 32 from the outside. Like reaction container 22, titration container 32 is of generally test tube-shape and is made of material which is sufficiently resilient to recover its shape after being squeezed sufficiently to crush the frangible ampule contained therein, and sufficiently transparent to permit the user to observe conditions and colors within the containers. Containers 22 and 32 may, as noted above, be made of any suitable resilient material, e.g., polyethylene, and may be identical to eliminate the need to stock and provide two different types of container, even though a volume-indicating mark (described below) required on container 32 is not needed, but is not inconvenient, on container 22. The caps 24 and 33 used on, respectively, containers 22 and 32 may be differently colored to facilitate following instructions which may form part of the test kit.

Titration container 32, like reaction container 22, has threads 32b formed adjacent to its mouth 32a so that container 32 can be sealed by a screw-on cap 33, thus sealing liquid extractant 42 inside titration container 32 until the user is ready to pour the extractant 42 into reaction container 22. Preferably, the extractant 42 is an aqueous solution which may contain an emulsion-breaker, e.g., 7 ml of 1% Na.sub.2 S0.sub.4 in water, to provide a solution in which the acidic species is soluble and is immiscible with the sample phase comprising the solvated oil sample. The sodium sulfate serves to inhibit the tendency of any surfactants which may be in the sample phase to lead to the formation of an oil-extractant emulsion. Caps 24 and 33 are removed from, respectively, containers 22 and 32 and the premeasured quantity of extractant is poured from titration container 32 into reaction container 22 containing the sample phase, taking care not to permit ampule holder 36 to spill out of titration container 32. Cap 24 is then replaced on container 22 with valve spout 24a closed so that the contents of container 22 can be vigorously mixed by shaking container 22. After shaking, the container 22 is vented by unscrewing and then retightening cap 24. Cap 33 may be replaced on titration container 32 to preclude contamination. Any acidic species not consumed by reaction with the basic species present in the sample phase is thus extracted into the aqueous extractant layer. Container 22 is then inverted with valve spout 24a still in the closed position, and the immiscible extractant is allowed to separate from the sample phase, the extractant phase forming as a bottom layer immediately adjacent to cap 24 and the sample phase, being less dense than the extractant phase, rising to a top layer within reaction container 22. The flat configuration of top 24d enables the user to place reaction container 22 with top 24d resting on any convenient flat surface where container 22 is left undisturbed to allow the mixture therein to separate into the separate aqueous extractant and sample phase layers. The emulsion-breaker provides a faster separation of the aqueous and sample phase layers; phase separation is typically achieved in about three minutes. The sample phase, being of lower density than the extractant phase, remains as a separated layer floating on, i.e., above, the extractant phase.

After the two phases have separated into distinct layers, a fixed quantity of the acid-containing extractant is introduced from reaction container 22 into titration container 32 through a filter funnel 48 (FIG. 4). This is accomplished by removing cap 33 from titration container 32 and inserting funnel spout 48b of filter funnel 48 into the mouth of titration container 32, and introducing extractant from reaction container 22. Reaction container 22 is picked up gently, to avoid re-mixing the separated phases, and while being kept inverted, i.e., with cap 24 facing downwardly, gently opening valve spout 24a and delivering a stream of the extractant layer into funnel mouth 48a by gently squeezing the exterior of container 22, to force extractant phase through conduits 24c and 24b of cap 24, thence through filter funnel 48 and into titration container 32, to the volume indicator provided by rib 34 which, in the illustrated embodiment (FIG. 3), indicates a volume of 5 ml. If it is necessary to squeeze the container 22 more than once in order to dispense the necessary amount of extractant phase, the container 22 is gently and slowly released between squeezes so that the solvated oil and extracted layers are not mixed by re-entering air. Container 22 may be discarded at this point. The extractant is seen to be physically separated from the sample phase promptly upon phase separation being attained. This eliminates absorption into the extractant of oil or components of the oil sample which might interfere with the accuracy of the titration, as might occur if the separated solvated oil and extractant layers were separated into phases but the phases were allowed to remain in contact with each other at the phase boundary. As an added precaution a filter is used, filter funnel 48 containing a filter material such as a polypropylene felt plug 48c to trap any minute quantities of organic contaminants such as oil, which may be suspended in the extractant phase.

As noted above, the amount of extractant provided is greater than that which must be transferred to titration container 32. This enables leaving behind within reaction container 22 enough extractant phase to keep the sample phase floating above and out of contact with cap 24 while reaction container 22 is inverted, thereby preventing the passage of any of the sample phase into titration container 32. The titration is thus carried out in an environment which is physically separate from the sample phase. When the measured amount of extractant phase is delivered into titration container 32, cap 33 is then replaced on container 32 and the measured amount of pH indicator is then released into the measured quantity of extractant phase contained in container 32 by squeezing container 32 from the outside to crush third frangible ampule 38 which contains the pH indicator, and shaking titration container 32 to mix the pH indicator with the measured amount of extractant phase.

Once the pH indicator has been added to the fixed amount of extractant in titration container 32, which is an environment free of the usually opaque oil sample being tested, the user may readily observe the condition of the indicator to determine the pH level of the extractant and thus determine the quantity of basic species present in the oil sample tested. This observation is advantageously accomplished by titration, so that the total base number of the sample oil can be quantitatively determined. For this purpose, the test kit includes a titration syringe 50 (FIG. 5) which contains a titration liquid, in this case an aqueous solution of a basic species, such as an aqueous solution of a strong base, e.g., NaOH or KOH. The titration liquid is added to the extractant until the pH indicator reaches its end point. The quantity of basic solution thus delivered to the extractant is indicative of the total base number of the oil sample tested.

In the illustrated embodiment, titration syringe 50 contains an aqueous solution of sodium hydroxide, for example, 1 ml of 0.064N NaOH, as the titration liquid. Titration syringe 50 is advantageously made from a molded plastic material and generally comprises a conventional cylindrical body 52 having a discharge spout 54 which is closed by a break-away closure tip 53 which closes off the discharge spout 54. A plunger head 58 is slidably received within body 52 at the end of body 52 furthest removed from discharge spout 54. Plunger head 58 is snugly received within body 52 and has sealing collars 58a and 58b which provide a liquid-tight seal within body 52 so that a titration liquid is sealed within body 52, between plunger head 58 and closure tip 53. The plunger 51 (FIG. 5A) of the titration syringe is conveniently provided separately, that is, not mounted in the plunger head 58. This shortens the length of titration syringe 50 for packaging and shipment.

Threaded syringe cap 56 is slidably mounted on the body 52 of titration syringe 50. Threads 56a of cap 56 are dimensioned and configured to be threadably received on the threads 32b of titration container 32, so that syringe 50 may be mounted upon container 32 with discharge spout 54 thereof positioned within titration container 32. The diameter of ampule holder 36 is small enough relative to the inside diameter of titration container 32 that ampule holder 36 would not impede the insertion of the body 52 of syringe 50 within titration container 32.

Plunger 51 is sized to be received within body 52 of titration syringe 50 and has an insertion tip 51a (FIG. 5A) which is dimensioned and configured to be snap-fitted within cavity 58c of plunger head 58. Titration syringe 50 has applied thereto graduations 55 which are scaled and numbered to directly correspond to the total base number of a tested oil sample as indicated by the volume of titration liquid (in this case a basic solution, e.g., an aqueous solution of NaOH) required to titrate the extractant to the indicator end point. In the case of the specific reagents exemplified in the foregoing description and 1% methyl red in alcohol used as the pH indicator, the end point is seen as a change in color from magenta to yellow. Therefore, when the user employs titration syringe 50 to titrate the extractant phase to the end point of the pH indicator, the number of the graduation at which plunger 51 comes to rest gives the total base number of the oil sample. This obviates the need for the user to perform any calculations to determine the total base number of the sample. Alternatively, the kit may comprise a color chart giving the pH and/or the total base number of the sample when the pH indicator attains a particular color shade. This latter technique is somewhat subjective and generally not as accurate as the use of graduations on the titration syringe. Generally, the use of a titration liquid as opposed to premeasured quantities of titer enables use of infinitely small increments of titer and a correspondingly more accurate test.

In the illustrated embodiment, which was used for the following Examples, the numbered graduations on the titration syringe indicate 0.5 milliliter ("ml") increments of the basic solution in the syringe. Unnumbered lines indicate equal volume increments between the numbered graduations. The direct reading TBN scale 55 is as follows:

  ______________________________________                                    
            ml of Basic                                                        
            Titration Solution                                                 
                      TBN                                                      
     ______________________________________                                    
            0.0       20                                                       
            0.1       18                                                       
            0.2       16                                                       
            0.3       14                                                       
            0.4       12                                                       
            0.5       10                                                       
            0.6        8                                                       
            0.7        6                                                       
            0.8        4                                                       
            0.9        2                                                       
            1.0        0                                                       
     ______________________________________                                    

When the user is ready to carry out the titration step, container 32 is shaken to thoroughly mix the pH indicator released from ampule 38 and the extractant phase. The user then places the insertion tip 51a of plunger 51 into cavity 58c of the plunger head 58 and snaps insertion tip 51a into place. Then, the user removes cap 33 from container 32, breaks off closure tip 53 of titration syringe 50, inserts discharge spout 54 into titration container 32, and screws cap 56 into place on the threads 32b of titration container 32. Plunger head 58, as noted above, is positioned within and seals the top (as viewed in FIG. 5) of body 52 of syringe 50. The opening resulting from breaking tip 53 is small enough so that there is no leakage of titration liquid before plunger 51 is operated. With this arrangement, in which cap 56 seals titration container 32, the titration may be performed without the risk of spilling any titration solution or extractant even while gently shaking titration container 32 as titration liquid is added, in order to completely mix the titration liquid with the contents of titration container 32. The user then performs the titration by slowly depressing plunger 51 of titration syringe 50 to expel the basic titration solution from syringe 50 into container 32, while constantly gently shaking container 32. Occurrence of the end point is indicated by a color change; in the specific case exemplified, by a color change from magenta to yellow. The resistance offered by the tight fit of plunger head 58 within the body 52 of titration syringe 50 holds the plunger 51 in place at the point where the user stops pushing it to expel the titration solution. This permits the user to easily read the TBN value directly from the graduation 55 printed on body 52 by noting the graduation at the bottom or forward end 58d of plunger head 58. In FIG. 5, plunger 51 is illustrated as being advanced somewhat more than half of its total travel distance. If the titration end point occurred at this point, the total base number would be read by the user at the point on the graduations marked by the forward end 58d of plunger head 58, as indicated by arrow TBN in FIG. 5.

The following examples illustrate the efficacy of an apparatus such as that described in Example 1 in determining total base number as compared to laboratory tests carried out on samples of the identical oils tested by use of the illustrated field test kit.

Example 1

A commercially successful field test kit in accordance with one embodiment of the present invention is sold under the trademark TITRA-LUBE TBN by Dexsil Corporation of Hamden, Connecticut, the assignee of this application. This kit contains reaction and titration test tube-shaped resilient containers and screw-on caps, a sampling syringe, a filter funnel and a titration syringe substantially as illustrated in FIGS. 1-5A, as well as a small tissue for wiping clean the exterior of the sampling syringe. The kit is packaged in a small cardboard box which includes a hollow box channel formed from heavy paperboard and having a pair of spaced-apart holes formed therein which are dimensioned and configured to receive and hold the test tube-shaped reaction and titration containers in the manner of a test tube rack. This field test kit contains the following components, which are numbered to correspond to the FIGS., in addition to the absorbent tissue wipe and other elements illustrated in the FIGS. The field test kit contains a sampling syringe 10 of 0.37 ml sample capacity, a reaction container 22 and its closure cap 24, a frangible glass ampule 28 containing 1.0 ml of isooctane, a frangible glass ampule 30 containing 1.0 ml of 0.114N HCl in isopropyl alcohol, a titration container 32 and its closure cap 33, a frangible glass ampule 38 containing 0.2 ml of 1% methyl red in alcohol, seven ml of 1% Na.sub.2 S0.sub.4 aqueous extractant 42, a filter funnel 48, a sealed titration syringe 50 containing 1 ml of 0.064N NaOH aqueous solution, and a plunger 51 for use as part of titration syringe 50.

A comparable test kit for testing the total acid number of an oil sample would be identical to that described above for testing the total base number, except that instead of hydrochloric acid in an alcohol vehicle it would include a strong base, such as potassium hydroxide, in an alcohol vehicle and the titration liquid would be a suitable acidic species such as an aqueous solution of hydrochloric acid.

Example 2

Part A. A number of new, i.e., unused, lubricating oils which are commercially available were sampled and tested to determine their total base number both by the American Society for Testing and Materials ("ASTM") Test Standard D 2896-88 and by utilizing the field test kit of Example 1.

The laboratory test described in ASTM Standard D 2896-88, which is published by the ASTM Committee on Standards, 1916 Race Street, Philadelphia, Pa. 19103, is incorporated by reference herein. This standard test utilizes perchloric acid as the acidic species and dissolves the sample in an essentially anhydrous mixture of chlorobenzene and glacial acetic acid. The sample is titrated with a solution of perchloric acid in glacial acetic acid with a potentiometric titrimeter. A glass indicating electrode and a calomel reference electrode are used, the latter being connected with the sample solution by means of a salt bridge. Meter readings are plotted against the respective volumes of titration solvent, and the end point is taken at the inflection in the resulting curve. This ASTM standard provides for both a Procedure A which utilizes 120 ml of titration solvent and a Procedure B which utilizes 60 ml of titration solvent. In carrying out tests of this Example 2, Procedure B was employed as was an Orion Model 960 titrator.

The field test kit in accordance with an embodiment of the present invention was utilized as described above on samples of the same oils tested by the ASTM method. The results given by the ASTM test are given to two decimal places and that by the field test kit to one decimal place in the following TABLE I.

                TABLE I                                                     
     ______________________________________                                    
                        TBN Number As Determined                               
     Lubricating Oil    By Test Method Of:                                     
     Sample                 ASTM     Ex. 1                                     
     No.      Description   D 2896-88                                          
                                     Field Test Kit                            
     ______________________________________                                    
     1A       Amalie        12.09    12.6                                      
     2A       Quaker State  8.72     8.7                                       
              (SAE-30W)                                                        
     3A       Quaker State HD                                                  
                            8.08     8.2                                       
              (20W-20)                                                         
     4A       Castrol GTX   7.84     7.2                                       
              (10W-40)                                                         
     5A       Castrol Motorcycle                                               
                            6.43     5.8                                       
     6A       Kendall Super 10.95    10.4                                      
              D III                                                            
     7A       Penzoil Multi High                                               
                            9.08     8.8                                       
              Viscosity (10W-30)                                               
     8A       Amoco LDO All 8.95     8.5                                       
              Seasons (20W-50)                                                 
     9A       Mobil 1 (15W-50)                                                 
                            7.05     7.4                                       
     ______________________________________                                    

Part B. Similar tests were conducted on used lubricating oils and the results obtained by the same two respective test methods are set forth in the following TABLE II. The brand names of the used oils of TABLE II are not known, but these samples comprised used crankcase oils taken from diesel engines operated by a number of different users.

  ______________________________________                                    
                  TBN Number As Determined                                     
                  By Test Method Of:                                           
     Lucricating Oil                                                           
                    ASTM      Ex. 1                                            
     Sample No.     D 2896-88 Field Test Kit                                   
     ______________________________________                                    
     1B             8.17      7.2                                              
     2B             6.93      6.6                                              
     3B             6.48      6.2                                              
     4B             7.24      6.5                                              
     5B             5.45      5.9                                              
     6B             9.29      9.0                                              
     7B             7.39      5.7                                              
     8B             8.37      7.5                                              
     9B             16.10     16.4                                             
     10B            13.40     12.8                                             
     ______________________________________                                    

It will be noted from TABLES I and II above that the field test kit in accordance with one embodiment of the present invention uniformly provided TBN results which closely correlated those provided by a sophisticated laboratory procedure. The data of TABLES I and II show that in those cases wherein the difference in TBN determined by the two tests was the greatest (Samples 4A, 5A, 1B, 4B, 7B and 8B), the exemplified field test kit provided a uniformly lower TBN number than that provided by the laboratory analysis, thus providing a safety factor in that it underreported rather than over-reported the TBN number as compared to the laboratory test. As is well known, because ASTM Test Method D 2896-88 uses perchloric acid, a very strong acid, it reacts with even the weakest basic species (which are very poor at neutralizing acidic combustion byproducts) present in the sample. The result is that test method D 2896-88 over-estimates the usable TBN. For example, ASTM Test Method D 4739-87, which employs hydrochloric acid as the acidic species, yields a lower TBN for a given sample than does ASTM D 2896-88, by as much as 2 to 3 TBN units on some used oils, and reflects the usable TBN more accurately. Nonetheless, the data show that the results between the two tests are closely comparable, indicating the reliability of the disposable, field test kit which is usable by untrained persons whereas a skilled laboratory technician is required to use relatively sophisticated equipment to carry out the ASTM test. The kit is referred to as "disposable" because it can be manufactured at relatively low cost and may be economically used and discarded after the single use for which it is designed.

While the invention has been described in detail with reference to specific embodiments thereof, it will be apparent that upon a reading and understanding of the foregoing, numerous alterations to the described embodiment will occur to those skilled in the art and it is intended to include such alterations within the scope of the appended claims. For example, the various stated volumes and concentrations of reagents, i.e., the volume of sample oil, the predetermined quantity of acidic species, the predetermined quantity of extractant mixed with the oil and used for titration may all be varied, as will be appreciated by those skilled in the art, as long as appropriate compensations relating to the concentration of, e.g., the acidic species and the basic solution in the titration syringe, are made. Further, the invention is not limited to the specific acidic species, basic titration solution or pH indicator; these may also be varied within the scope of the present invention by those skilled in the art. Finally, the invention is not limited to the employment of an aqueous extractant phase; other extractants which perform substantially in the same way to achieve the same result may likewise be used.

Claims

1. An apparatus for determining the quantity of acidic or basic resident species present in an oil sample, the apparatus comprising:

(a) sampling means for drawing a predetermined quantity of oil as a sample and introducing the sample into a reaction container;
(b) a container system comprising:
(i) a reactant container containing a predetermined quantity of a reactant species comprising one of an acidic species and a basic species, for reacting with a basic or acidic resident species in the sample, if any;
(ii) an extractant container containing a predetermined quantity of an extractant in which the reactant species is soluble but which is immiscible with the sample, for extracting unreacted reactant species from the sample; and
(iii) at least one reaction container dimensioned for receiving the sample from the sampling means and for receiving the predetermined quantity of the reactant species, to allow the reactant species to be mixed with the sample, and for receiving the extractant to allow the extractant to be mixed with, and to separate from, the sample to extract the unreacted reactant species from the sample;
(c) pH measuring means for determining the pH of the extractant; wherein the pH measuring means comprises:
(d) a titration syringe containing a titrant for the reactant species, for titrating a predetermined quantity of the extractant having unreacted reactant species therein; and
(e) an indicator container containing a titration end point indicator for indicating the end point of the titration of the extractant with the titrant; wherein the at least one reaction container is dimensioned for further receiving the titrant and the end point indicator; and wherein the titration syringe bears graduations that are scaled and labeled to indicate one of the total base number and total acid number of the sample at the end point of the titration of reactant species in such predetermined quantity of extractant after reaction of said predetermined quantity of the reactant species with a sample drawn with the sampling means and extraction of remaining reactant therefrom by the extractant.

2. The apparatus of claim 1 wherein at least one of the reactant container and the extractant container comprises a frangible ampule.

3. The apparatus of claim 1 further comprising a solvent container containing a premeasured quantity of a solvent for mixing with the sample to produce a solvent phase to which the reactant species is added.

4. The apparatus of claim 1 comprising a second reaction container for receiving and holding the extractant, the titrant and the titration end point indicator separate from the sample during the titration.

Referenced Cited
U.S. Patent Documents
3030190 April 1962 Seemann et al.
3193356 July 1965 Smith et al.
3259463 July 1966 Feasley et al.
3410664 November 1968 Fielding
3510260 May 1970 Krawetz et al.
3653838 April 1972 Glass
3653839 April 1972 Luks et al.
3808149 April 1974 Ellis et al.
3811837 May 1974 Hoffman
3873274 March 1975 Neisius
4154670 May 15, 1979 Forsberg
4203725 May 20, 1980 Snowden, Jr. et al.
4238197 December 9, 1980 Eisentraut et al.
4269604 May 26, 1981 Snowden, Jr.
4405448 September 20, 1983 Googin et al.
4430208 February 7, 1984 Pytlewski et al.
4477354 October 16, 1984 Fessler
4557899 December 10, 1985 Schoonover et al.
4686192 August 11, 1987 Fisher
4731332 March 15, 1988 Blumenthal et al.
4735905 April 5, 1988 Parker
4873056 October 10, 1989 Fisher
4925627 May 15, 1990 Johnson
4962039 October 9, 1990 Benedyk
5013667 May 7, 1991 Lynn et al.
5028543 July 2, 1991 Finch et al.
5055410 October 8, 1991 Blumenthal et al.
Foreign Patent Documents
0170466 February 1986 EPX
3401258 August 1984 DEX
5924384 June 1977 JPX
5449198 September 1977 JPX
Other references
  • Am. Soc. for Testing & Materials, ASTM D 664-89, "Standard Test Method for Acid Number of Petroleum Products by Potentiometric Titration", Jan. 1990. Am. Soc. for Testing & Materials, ASTM D 2896-88, "Standard Test Method for Base Number of Petroleum Products by Potentiometric Perchloric Acid Titration", Jan. 1989. Am. Soc. for Testing & Materials, ASTM D 974-87, "Standard Test Method for Acid and Base Number by Color-Indicator Titration", Dec. 1987. Barnes, J.R., "Importance of Railroad Diesel Engine Oil TBN and its Relevance to LMOA Generation 5 for Salicylate Oils", Lubrication Engineering, vol. 47, 9, 713-722, Oct. 1990. Amer. Soc. for Testing & Materials; ASTM D 4739-87; Standard Test Method for Base Number Determination by Potentiometric Titration; Dec. 1987.
Patent History
Patent number: 5800782
Type: Grant
Filed: Sep 12, 1996
Date of Patent: Sep 1, 1998
Assignee: Dexsil Corporation (Hamden, CT)
Inventors: Richard A. Hagstrom (Cheshire, CT), Stephen R. Finch (Concord, NH), Timothy D. Lynn (Hamden, CT)
Primary Examiner: Harold Y. Pyon
Attorneys: Law Office of Victor E. Libert, Law Office of Victor E. Libert
Application Number: 8/712,969